1. Field
The following description relates to a level shifter, such as, for example, a level shifter capable of converting a low-voltage input signal into a high-voltage output signal without using a high-voltage transistor.
2. Description of Related Art
A system on chip (SOC) that implements a circuit system typically includes various semiconductor circuits that are integrated on a single chip. A SOC is conventionally designed such that high-performance blocks use a high voltage and low-performance blocks use a low voltage in order to save energy. However, because different voltages are used in neighboring blocks, a leakage current may develop or malfunction may occur in an interface area between the blocks.
To reduce the occurrence of malfunction, a level shifter may be used as an interface circuit that adjusts voltage levels between the blocks. A level shifter converts a voltage supplied from an outside into a higher voltage or a lower voltage, depending on a voltage used in the block.
In a conventional device, a plurality of level shifters connected in series is used to convert a low-voltage signal supplied from an outside into a high-voltage signal, for example.
Hereinafter, an operation of a level shifter is described with reference to FIG. 6.
The level shifter illustrated in FIG. 6 converts a low-voltage signal of 0 V to 1.5 V into a high-voltage signal of 5V to 10V.
Referring to FIG. 6, first, the low-voltage signal of 0 V to 1.5V is converted a normal-voltage signal of 0 V to 5V, using a first-level shifter unit constituting of a medium-voltage transistor. The medium-voltage transistor used in this level shifter unit is a transistor having VGS and VDS voltages of 6 V or less.
Next, the normal-voltage signal of 0 V to 5 V is converted into a high-voltage signal of 0 V to 10 V, using a second-level shifter unit constituting of a high-voltage transistor. The high-voltage transistor used in this level shifter unit is a transistor having VGS and VDS voltages of 6 V or more.
Finally, the high-voltage signal of 0 V to 10 V is converted into a high-voltage signal of 5 V to 10 V, using a third-level shifter unit constituting of a high-voltage transistor.
The first-level, second-level and third-level shifter units may occupy a substantial area on a chip in order to convert a low-voltage signal into a high-voltage signal. Further, when a fabrication process that does not support a transistor having the VGS voltage of 6 V or more is used, it is difficult to fabricate the level shifter.